Disclosed are a novel sulfonic acid derivative compound and a novel naphthalic acid derivative compound with high solubility in organic solvents, good photosensitivity, and suitability as a photoacid generator and a polymerization initiator. The sulfonic acid derivative compound is represented by the formula (I)
(wherein R
01
, R
04
, R
05
, and R
06
represent a hydrogen atom; any one of R
02
and R
03
represents an alkoxy group having a carbon number of 4 to 18 which may be substituted with an alicyclic hydrocarbon group, a heterocyclic group, or a halogen atom and which may have a branch, or the like; and R
07
represents an aliphatic hydrocarbon group having a carbon number of 1 to 18 which may be substituted with a halogen atom and/or an alkylthio group, or the like).